Gun boresight



1958 N. E. SPURLING 2,819,527

GUN BORESIGHT Filed March 7, 1955 INVENTOR NELSON E. SPURLING W 5 62/3 W ATTORNEYS United States Patent GUN BORESIGHT Nelson E. Spurling, Valparaiso, Fla.

Application March 7, 1955, Serial No. 492,813

5 Claims. (CI. 33-46) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payinent of any royalties thereon or therefor.

This invention relates to a gun boresight and more particularly to a gun boresight adapted for insertion into the muzzle of a gun bore to check the accuracy of the standard sight system of the gun.

In boresighting practice a distant object is viewed through the bore of a gun barrel and the line of sight is compared with the line of sight taken by aim on the sight target from the adjunctive sighting system of the particular gun under study. customarily, boresights have used the center line of the entire length of gun bore on which to align the optical axis of the boresight, or have utilized a portion of the gun bore within which to align the optical axis of the sight which, when extended, did not represent the true path of a projectile as it leaves the gun barrel. Although a fair estimate of the accuracy of the sighting system of the gun may be obtained by alignment of the boresight optical axis on the longitudinal center line of a gun bore, it has been found that only by mounting a gun boresight in the last few calibers of the muzzle of a gun bore with its optical axis in coincidence with the center line of this muzzle portion of the gun bore may the most true accuracy of the gun sighting system be established.

Known mechanical designs of boresights usually permit only a small area of the boresight structure to be utilized to align the optical axis of the boresight with the center line of the gun barrel. Some few boresights do include a cylindrical mounting structure which must be machined to the exact caliber of the bore in order that contact may be established between the mounting structure and the bore such that the boresight is stabilized in the bore in a desirable position. However, in such designs the optical system of the boresight is not made coincident with the center line of the gun barrel. at the muzzle portion of the gun bore, and, in many instances, not even parallel with the center line of the gun bore at this critical area of the bore.

The instant invention overcomes the above-mentioned objectionable features of the known boresights by the provision of a boresight which permits the gun barrel center line for the few calibers nearest the muzzle to be optically projected into space. The boresight is snugly positioned in that portion of the gun bore which has the last contact with a projectile by means of an expandable sleeve mounting member which is adapted to cause the boresight optical axis to coincide with the center line of the muzzle section of the bore when adjusted to boresighting position. I

An object of the present invention is the provision of a boresight having a reticle within the optical system of the device which is collimated at assembly to coincide with the mechanical center line of the telescope lens arrangement whereby an object when viewed through the ice reticle is assured of being intercepted by the optical axis of the boresight.

Another object is to provide a boresight having a mounting structure which enables uniform clamping of the boresight within the muzzle of a gun bore such that the longitudinal axis of the telescope is positioned along the gun bore center line at the gun muzzle which will enable the gun to be aimed at a desired point in space with exactness.

A further object of the invention is the provision of a boresight having adjustable mounting structure which enables simple but precise mounting techniqueto be employed to position the boresight within the last few calibers of a gun bore with the boresight optical axis in coincidence with the center line of the last few calibers of the bore.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 is a longitudinalsectional view of one embodiment of the device mounted in the last few calibers of a gun bore;

Fig. 2 is a front view, slightly enlarged, of the reticle of the lens system shown in Fig. l; and v Fig. 3 is a reduced perspective view of the collet utilized in the mounting shown in Fig. 1.

There is shown in Fig. 1 a preferred embodiment comprising a boresight 11 mounted to extend into the muzzle end of a gun bore 12 only for the last few calibers of the bore. Centrally positioned within bore 12 is a telescope 13 having a tubular housing 14 with terminal annular bell flanges 15 and 16, and a lens system, preferably achromatic, which may comprise the conventional double-convex objective lens 17 and double-convex ocular lenses 18 and 19. A reticle plate 21 is conveniently supported within housing 14 at approximately the final image focal plane.

Referring to Fig. 2 the reticle plate 21 is shown to include reticle lines 22 which are collimated at assembly to cause the mechanical center line of housing 14 and the principal axis of the lens system 17,18, and ,19 to pass through the intersection 23 of reticle lines 22. By adapting the intersection 23 of the reticle lines 221:0 lie on the mechanical axis of housing 14 and the optical principal axis of the boresight lens system 17, 18, and

19, the aim taken on a distant object through the bore by the superposition of reticle lines 22 on the object theoretically projects the optical principal axis and the mechanical center line of housing 14 into space to establish a true line of sight to the object from the bore. By the provision of the reticle 21 and lines 22 in its relative position with the axes of housing 14 and lens system 17, 18, and 19, the boresight 12 may be used by different individuals with uniformly accurate results since the reticle lines 22 cause different observers to view.

a single aiming point at a common observation station. The eye lens is of customary design, and is mounted either as a simple ocular lens or as a part of a viewing attach-. ment in the breech of the gun barrel, for example. Thus, it can be seen that the gun barrel servesthe purpose of a telescope body as the result of using both ends of the barrel for mounting lens elements.

A cylindrical collet 24 is slidably and concentrically positioned about a portion 25 of tube housing 14 which is to be inserted into the muzzle of a gun bore, and is formed with an inwardly directed annular wedge 26 at its inner end to engage the bell flange 16 of housing 14, and with another inwardly directed annular wedge 27 formed at its outer end. A tapered collar 28 is threadedly 3 engaged" to the tubular housing 14 and is longitudinally movable into engagement with wedge 27.

Collet 24, as best shown in Fig. 3, is provided with longitudinal slots 29. which extend from each end of the collet toward the center of the collet. These slots are provided to permit expansion of each end of the collet into a firm holding relationship with the interior of bore 12 when collar 28 is turned to engage wedge 27. As collar 28 is turned to engage wedge 27, wedge 26 is, engagedby bell flange 16. A circumferential skirt 31 at the outer end of collet 24 acts as a stop; to allow the collet to be inserted into a gun bore only for the last few calibers thereof.

In use collet 24 and housing 14, assembled together, are inserted into the muzzle of a gun bore 12 for the last few calibers of the gun barrel which have the most effect on the final trajectory of'a bullet. Collet 24 is inserted into, the bore 12- to a depth determined by skirt 31. Tapered collar 28 is then turned to move longitudinally into. wedging engagement with wedge 27 which action simultaneously causes wedge 26 to engage bell flange 16 of housing 14. By the provision of longitudinally extending slots 29 in collet 24, the ends of the collet are expanded to firmly engage the bore 12, thereby axially positioning housing 14 into coincidence with the mean center line of that portion of the bore. A conventional eyepiece or ocular lens, not shown, is inserted into the breech of the gun, for example, for viewing the objective through the lens system 17, 18, 19 and the reticle plate 21. Since the housing 14 center line is aligned with the principal axis of the boresight lens system 17, 18, and 19 fixed within housing 14, and reticle lines 22 visually aid an observer to View a line of sight coincident with these axes, a boresight at an aimed point assures true aiming of the barrel whereby a bullet which leaves the bore will travel to the desired target.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A boresight for guns comprising; a telescope having a tubular housing and a lens system with a reticle collimated on the optical principal axis coincident with the longitudinal center line of the tubular housing, the housing of said telescope being formed with circumferential bell flanges at each end thereof, an expandable sleeve coaxially and slidably mounted on the tubular housing of said telescope intermediate the ends thereof, said sleeve having, inwardly sloping wedge flanges formed on the inner surface at each end thereof, and means mounted on the tubular housing of said telescope to engage one of said wedge flanges to expand said sleeve to the inner surface of a gun bore and to fix said telescope in boresighting nosition within said sleeve.

2. boresight for gun bores comprising; a telescope having a tubular housing and a lens system with a reticle collimated on the optical principal axis coincident with the longitudinal center line of the tubular housing, the housing of said telescope being formed with circumferential bell flanges at each end thereof, a tubular sleeve having longitudinal slots provided therein coaxially and slidably mounted on the tubular housing of said telescope intermediate the ends thereof, said sleeve having inwardly sloping wedge flanges formed on the inner surface at each end thereof, and a cylindrical collar threadedly engaged on the outer surface of the tubular housing of said telescope whereby said collar may be turned to expand said sleeve to lock said telescope in boresighting position.

3. A boresight for gun bores comprising; a telescope having a tubular housing and a lens system with a reticle collimated on the optical principal axis coincident with the longitudinal center line ofthe tubular housing, the tubular housing of said telescope having an inner bell flange and an outer bell flange formed at the extremities thereof, an expandable collet receivable into a gun bore axially and slidably mounted to surround the housing of said telescope intermediate the extremities thereof and having inwardly sloping wedge flanges formed on the inner surface at each end of said collet and a circumferential skirt flange at the outer end thereof, a collar rotatably engaged for longitudinal movement on the outer surface of the housing of said telescope and having an inwardly directed frustro-conical surface to slidably mate with the wedge flange at one end of said collet and to longitudinally move, the housing of said telescope to slidably mate the other wedge flange of said collet with the inner bell flange of the housing of said telescope whereby the telescope may be fixed within the bore of a gun in boresighting; position.

4. An expandable housing. assembly for boresighting, telescopes suitable for. mounting within a gun barrel muzzle, comprising; a tubular housing adapted to support a telescopic lens system therein, said housing having an inner bell-flange andan outer bell flange formed at the, extremities thereof, an expandable collet receivable into a gun bore axially and slidably mounted to surround the housing intermediate the extremities thereof and having inwardly sloping wedge flanges formed on the inner surface at eachend of the collet and a circumferential skirt flange atthe outer end thereof, a collar rotatably engaged for longitudinal movement on the outer surface of the housing and having an inwardly directed frustro-conical surface to slidably mate with the wedge flange at one end of said collet and to longitudinally move the housing of said telescope to slidably mate the other wedge flange of said collet with the inner bell flange of the housing whereby the assembly may be fixed within the bore of a gun in boresighting position.

5. A bore engaging expandable housing assembly comprising a tubular housing having a first and a second bell flange formed at the extremities thereof, a sleeve member slidably mounted on the tubular housing intermediate the bell flanges, said member having longitudinal slots extending from both ends toward the middle portion of the sleeve to allow expansion of the sleeve member at the end portions, thereof, the inner surface of said sleeve member having formed adjacent the ends thereof first and second wedge portions with inclined surfacesv sloping outwardly from the sleeve, member, the first wedge portion being shaped complementary to the first bell flange of said housing for frictional engagement therewith, a collar engaged for axial movement on the housing and into wedging engagement with the second wedge portion of said sleeve member in such a manner that the sleeve member is caused to expand at one end portion by the coaction of the first wedge portion and the first bell flange of the housing, and the other end of the sleeve member is caused to ex pand simultaneously with the first wedge flange by axial movement of the collar within the second wedge portion of said sleeve member.

References Cited in the file of this patent UNITED STATES PATENTS 1,005,928 Bergstrom Oct. 17, 19.11 1,232,704 Maloy July 10, 1917 2,226,078 Spahn Dec. 24, 1940 2,294,913 Kaufman et al Sept. 8, 1942 2,360,968 Mundy Oct. 24, 1944 2,383,036 Benjamin et a1. Aug. 21, 1945 2,548,861 Brown Apr. 17, 1951 2,573,703 Gardner Nov. 6, 1951 

